Internal combustion engines and their accessories, such as an engine-driven cooling fan, emit an appreciable amount of noise or acoustical energy during operation thereof. Such energy is commonly measured by its level of intensity and its frequency range with the human being highly sensitive to frequencies in the range of from 800 Hz to 3,000 Hz. One approach to the dampening-down of the noise to an acceptable level is to provide the engine enclosure with a plurality of louvers mounted on one or more sides thereof with the louvers including acoustical material in the form of pads.
Although the louvers function efficiently to absorb a portion of the acoustical energy emitted from the engine, a substantial portion thereof is free to pass through airflow passages, necessarily defined between the louvers to permit ambient air to ingress into the engine enclosure for cooling purposes. In particular, the louvers are normally not constructed and arranged to be optically dense, when viewed from within the engine enclosure and only intercept and absorb a portion of the sound waves which represent the acoustical energy or noise.
In addition, conventional louver arrangements of the above type are somewhat bulky and exhibit relatively high space to sound absorption efficiency ratios.